The present invention generally relates to a heat exchanger. More particularly, the present invention pertains to a heat exchanger for controlling the temperature of fluid inks and other liquids containing emulsions, suspensions or dissolved solids.
Fluid inks are commonly used in the printing industry for flexographic printing and rotogravure printing. These fluid inks include water based fluid inks, solvent based fluid inks and ultraviolet curable inks. One important consideration in fluid ink printing is the viscosity of the fluid ink. The fluid ink should be maintained at a certain viscosity to avoid problems during the printing process and to optimize the printing process.
However, as the fluid ink is pumped to the printing deck, the ink becomes heated because of, for example, heat produced at the ink applicator, heat produced by hot air driers, the pumping of the fluid through the pump, and other sources as well. This heating of the fluid ink can be quite problematic. Water based fluid inks are typically stabilized by amines and at higher temperatures, the amines tend to evaporate. This causes the ink to become unstable.
Solvent based fluid inks commonly include a solvent which, when excessively heated, flashes off and causes the ink to become more viscous than desired for optimum printing quality. Also, health and environmental concerns arise when solvent based fluid ink is heated so that the solvent flashes off.
Ultraviolet curable inks are a bit different in that they are commonly made almost entirely of solids. Thus, these types of fluid inks must be heated to a specified temperature to ensure quality printing.
In each of the fluid inks mentioned above, it is thus desirable to maintain the temperature of the fluid ink at a generally constant temperature to help ensure optimum printing quality and avoid potential health and environmental concerns. Thus, it has been proposed to use a heat exchanger in an attempt to control the temperature of the fluid inks within a desired range. However, the heat exchangers typically used in this regard have been found to be susceptible of a variety of problems. Plate type heat exchangers and multi-tube heat exchangers possess many convoluted surfaces and welded seams that readily collect ink solids. Thus, when the operation of the printing deck is stopped so that the flow of ink through the heat exchanger ceases, ink can collect on these surface and dry. The resulting ink solids can be extremely difficult to remove from the heat exchangers.
Another type of heat exchanger that has been used in the past is a jacketed ink sump that involves the use of a double walled sump with a heat transfer fluid between the two walls. These types of heat exchangers are also quite difficult to clean and suffer from the additional disadvantage that they must typically be disconnected from the heat transfer supply source. Also, these types of heat exchangers are rather heavy, difficult to clean, and inefficient and not well suited to effecting adequate cooling.
A further type of heat exchanger that has been used in this context is one in which a cooling coil is located directly in the ink sump. This type of system tends to be rather cumbersome. Also, this system suffers from the disadvantage that the cooling coil must be cleaned, a task that can be quite time consuming and messy.
In light of the foregoing, a need exists for a heat exchanger that is able to maintain the temperature of fluid inks and other liquids containing emulsions, suspensions and dissolved solids at a substantially constant temperature while at the same time being easy to clean, compact in design and relatively simple in construction.
In accordance with one aspect of the invention, a fluid material application system for applying printing ink, adhesive or a coating to a paper product includes a fluid material source containing fluid material in the form of fluid ink, adhesive or a coating, a heat transfer fluid source containing heat transfer fluid, and a heat exchanger that includes a heat exchange element comprised of a hose for carrying the heat transfer fluid and a tube for carrying the fluid material. The tube is positioned within the hose and the heat exchange element possesses a winding configuration with adjacent portions of the heat exchange element resting on top of one another so that the adjacent portions are supported in a vertical fashion. An application deck is adapted to apply the fluid material to a paper product and a fluid material introduction conduit connects the fluid material source to the inlet of the tube to carry the fluid material from the fluid material source to the heat exchanger. A fluid material supply conduit connects the outlet of the tube to the application deck to carry fluid material from the heat exchanger to the application deck, a heat transfer fluid supply conduit connects the heat transfer fluid source to the inlet of the hose to carry heat transfer fluid to the heat exchange element, a heat transfer fluid return conduit connects the outlet of the hose to the heat transfer fluid source to carry heat transfer fluid from the heat exchange element to the heat transfer fluid source, and a fluid material return conduit connects the application deck to the fluid material source to return fluid material from the application deck to the fluid material source.
According to another aspect of the invention, a fluid material application system for applying one printing ink, adhesive or a coating to a substrate includes a fluid material source containing fluid material in the form of printing ink, adhesive or a coating, a heat transfer fluid source, and an application deck for applying the fluid material to a substrate, with the application deck being connected to the fluid material source. A heat exchange element is also provided and is comprised of a tube positioned within a hose so that the central axis of the tube is generally parallel to the central axis of the hose. The tube is connected to the fluid material source to carry the fluid material through the heat exchange element and the hose is connected to the heat transfer fluid source to carry heat transfer fluid through the heat exchange element.